Water Supply MCQ Quiz in मल्याळम - Objective Question with Answer for Water Supply - സൗജന്യ PDF ഡൗൺലോഡ് ചെയ്യുക

Concept:

Logistic curve method:

The logistic method is suitable for regions where the rate of increase or decrease of the population with time and also the population growth is likely to reach an ultimate saturation limit because of special local factors.

The population after any time from the start is given as,

\(P = \frac{{{P_s}}}{{1 + m{{\log }^{ - 1}}(nt)}}\)

Where, Ps = Saturation population

\({P_s} = \frac{{2{P_o}{P_1}{P_2} - P_1^2\left( {{P_o} + {P_2}} \right)}}{{{P_o}{P_2} - P_1^2}}\)

Where, Po, P1, and P2 are census data

Additional Information

Various methods for population forecasting as suitable for that city, considering the growth pattern, are as follows:

1. Arithmetical increase method:

• In this method assumed that the population is increasing at a constant rate.
• This method is suitable for a large and old city with considerable development.

2. Geometrical increase method (or geometrical progression method):

• In this method, the percentage increase in population from decade to decade is assumed to remain constant. 
• This method gives higher values and hence should be applied for a young and rapidly increasing city, but only for a few decades.

3. Incremental increase method:

• This method is a modification of the arithmetical increase method and it is suitable for an average size town under the normal condition where the growth rate is found to be in increasing order.

4. Logistic curve method:

• This method is used when the growth rate of the population due to births, deaths, and migrations takes place under normal situations and it is not subjected to any extraordinary changes like an epidemic, war, earthquake, or any natural disaster, etc.

Explanation:

            \(\overline x\) = Rate of population growth 

Solution:

Rate of population growth,  \(\overline x = \frac{x_{1}+x_{2}}{2} = \frac{0.1+.02}{2}= 0.15\) , 

Here n = 1 (i.e. 10 years)

\(P_{2011}=P_{2001}+ 1 \times \overline x\)  ⇒ \(P_{2011}=2.3+ 1 \times0.15 = 2.45 \ Lakhs\) 

Concept:-

Equivalent Method: - This method is used to convert the entire distribution system of pipes to equivalent pipe, which carries the discharge corresponding to the same head loss.

Hardy-Cross Method: - This method is used to find the discharges in the unknown pipes using the equation of continuity. It only calculates discharges and the method remains the same whether domestic supply or fire demand considered or not.

Electrical Analysis: - This method establishes the analogy between the flow of fluid and the flow of current. As per the electrical analysis, the greater is the resistance lesser will be the flow. Similarly, the greater the head loss, the lesser will be the flow of fluid.

Circle Method:- This method is used for the analysis of the distribution system in which domestic supply is neglected and fire demand is considered.

Concept:

Geometric incremental method: This method is suitable for young and rapidly developing cities as they record logarithmic or exponential increase in population.

If population increase is given per decade: Population after n decades (P_n) is given by

\({{\rm{P}}_{\rm{n}}} = {{\rm{P}}_{\rm{o}}} \times {\left( {1 + \frac{{\rm{r}}}{{100}}} \right)^{\rm{n}}}\)

where, P_n is population after ‘n’ number of decades; P_o is Initial population considered; n is number of decades and r is geometric rate constant per decade.

Calculation:

Given, initial population in 2000, P₀ = 82300; Rate of increase in population per decade, r = 35%; no of decades considered, n = 2.

∴ Population in 2020, \({{\rm{P}}_{2020}} = 82300 \times {\left( {1 + \frac{{35}}{{100}}} \right)^2} = 149991.75\; \approx 150000\)

Explanation:

Grid Iron System:

• It is suitable for cities with rectangular layout, where the water mains and branches are laid in rectangles.
• This system is also known as an interlaced system or reticulation system. 

• In this system, the mains, sub-mains, and branches are inter-connected with each other. Thus, this system provides free circulation of water through the pipelines.

• Cut-off valves are provided at each junction point. This is suitable for well-planned towns and cities.

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The advantages of the gridiron system are:

• In case of repairs, a very small portion of the distribution area will be affected.  
• This system provides free circulation of water through the pipelines. Hence, it is not liable for pollution due to the stagnation of water.  
• The head loss is minimum.
• It provides sufficient supply during fire fighting.

​Disadvantages of gridiron system are:

• This system requires more length of pipelines and a greater number of cut-off valves.
• Its construction is costlier.
• The design calculations are complicated and difficult.

Concept:

Geometric incremental method:

This method is suitable for young and rapidly developing cities as they record logarithmic or exponential increases in population.

If population increase is given per decade:

Population after n decades (Pn) is given by

\({{\rm{P}}_{\rm{n}}} = {P_o} \times {\left( {1 + \frac{r}{{100}}} \right)^n}\)

Calculation:

Given

Constant growth rate

r = (40 + 20) / 2 = 30%

The population in 4Th year(n = 1) is

\({{\rm{P}}_{\rm{4}}} = {P_o} \times {\left( {1 + \frac{r}{{100}}} \right)^n}\)

\({{\rm{P}}_{\rm{4}}} = {8400} \times {\left( {1 + \frac{30}{{100}}} \right)^1}\)

P₄ = 10920

Concepts:

The various IS codes nos and their usage are specified below in tabulated form:

Layout of Distribution System:

Pipes except the service connections are usually made of cast iron with some type of coating to avoid rusting where as foe service connection galvanised iron pipes are used.

Dead end system: Also known as tree system, it has one main pipe from which various submains bifurcate and from submains, laterals comes out.

It is easy to design, cheap and simple but due to dead ends, free circulation of water is prevented.

Grid-iron system: Here the mains, branches and laterals are interconnected hence dead ends are eliminated and water can reach to a location through more then one route. Pressure throughout the grid system is equal.

Ring system: It has main pipe all over the area. Thus, it has smaller branches and laterals, and has lesser number of valves. Hence cheaper as compared to grid system.

Radial system; A big area is divided into several zones and at the centre of each zone, a distribution reservoir is kept. Thus it has zonal distribution.

Explanation

Dead-end System:

• It is also called a tree system, it consists of one main supply line, from which originates (generally at right angles) a number of sub-main pipes; Each sub-main is then divided into several branch pipes, called laterals
• This type of distribution system is suitable for older towns that have developed in a haphazard manner, without properly planned roads e.g. old cities, irregularly grown cities, etc; It is economical and simple

​

Gridiron System:

• It is also known as an interlaced system or reticulation system, the mains, sub-mains, and branches are all connected with each other
• There is no dead-end in the system as looping is provided and is most suitable for well-planned cities.
• There is equal pressure in all pipes and multiple flow path.

Radial system:

• If a city or town is having a system of radial roads emerging from different centers, the pipeline can be best laid in a radial method by placing the distribution reservoir at these centers
• The water from the distribution reservoir is then supplied radially to distribution pipes and thus also known as zonal distribution

Ring System:

• It is also called a circular system; In this system, a closed ring, either circular or rectangular, of the main pipes, is formed around the area to be served.
• The distribution area is divided into rectangular or circular blocks, and the main water pipes are laid on the periphery of the blocks
• This system is very suitable for towns and cities having well-planned roads.
• It is economical and the pressure at the ends are reasonably equal

Concept:

(i) Average Daily Demand (q)

Average daily demand = (per capita average consumption in litre/person/day) × population

(ii) Maximum Daily Demand

Maximum daily demand = 1.8 × Avg. daily demand = 1.8 × q

(iii) Maximum Hourly Demand:

Maximum hourly demand of the maximum day i.e. Peak demand

= 1.5 × Avg hourly demand of the maximum day \(= 1.5 × \left[ {1.8 × \frac{q}{{24}}} \right] = 2.7\left[ {\frac{q}{{24}}} \right]\)= 2.7 × annual avg hourly demand

(iv) Monthly peak demand = 1.28 × monthly average demand

(v) Yearly peak = 1.0 × yearly average demand

Additional Information The percentage ratio of maximum demand to the average demand can be computed using Good Rich equation;

p = 180 × t-0.10

where

t = time(days)

Fluctuation in hourly demand is also termed as Peak factor which depends upon the population as follows;